Collaboration continued on three major epidemiologic studies: (1) a case-control study of childhood acute lymphoblastic leukemia examining electromagnetic fields and other residential exposures; (2) the Agricultural Health Study, a prospective study of a cohort of 75,000 adults living on farms in Iowa and North Carolina to investigate potential disease risks associated with agricultural exposures; and (3) the ALTS trial, a randomized trial to examine whether human papilloma virus DNA type can be used to determine the appropriate treatment for women with abnormal PAP smears. Studies of trends in breast cancer rates in the United States and Canada were conducted to examine geographic and racial differences in risk. Additional projects and studies for which assistance has been provided include: the creation of an atlas of cancer mortality maps showing the regional variation of cancer mortality rates in the United States; investigations of whether service in Vietnam is associated with increased risk of cancer in a large cohort of West Virginia veterans and in military working dogs; a study quantifying the risk of second cancers in a cohort of retinoblastoma survivors; investigations to determine if the frequency of stable aberration frequencies is related to chronic exposure to ionizing radiation in a U.S. cohort of radiologic technologists or in workers at the Sellafield British Nuclear Fuels facility; studies examining possible associations between HLA type and nasopharyngeal carcinoma risk or susceptibility to infection with Human T-cell Lymphotropic Virus type 1; a study to determine if specific mutations in the RB1 gene result in higher risk of second cancers; a study to identify gene mutations in patients with breast cancer who have additional primary cancers; a record linkage study of cancer risk following splenectomy; and studies of factors associated with seroreactivity to HPV-16 virus-like particles.